Monoclonal antibodies reactive to cell surface antigens of LT teratocarcinoma stem cells have been selected and purified by cloning. These antibodies will be used as reagents to study the cell surface molecules present on developing embryos and to identify molecules involved in cell-cell recognition of teratrocarcinoma embryonal cells and murine embryonic cells. LT teratocarcinoma embryonal cells form tumors exclusively in the gonads of many female mice. This specificity of metastasis is correlated with selective cell adhesion to cells of the target orgen. Monoclonal antibodies will be used to analyze this recognition in monolayer adhesion assays. The role of embryonic cell surface antigens in development may be suggested by determining the pattern of expression of embryonal antigens in developing embryos and adults. These will be studied by absorption analyses and quanitative immunofluorescence analyses using a fluorescence-activated cell sorter. It is the long term objective of these studies to identify and biochemically characterize molecules important in early embryonic recognition events, using monoclonal antibodies that interfere with cell adhesions to purify membrane components. The identification of molecules involved in specific recognitions of teratocarcinoma embryonal cells may be used to investigate the mechanisms tumor cells use to successfully metastasize.